End grain cuts of Kiawe wood create a unique and organic form.
Capstone Proposal
This capstone project investigates the ecological impacts and management of invasive Kiawe (Prosopis pallida) in Hawai‘i, with a focus on utilizing its wood for sand dune stabilization and construction materials. While Kiawe is typically considered an invasive species, its durable wood presents a unique opportunity for sustainable resource utilization. It has the potential for stabilizing sand dunes and reducing the reliance on costly imported materials for erosion control. This approach requires thoughtful environmental planning and design recommendations that account for site-specific geomorphic and hydrologic conditions (Bentrup & Hoag 1998, 30-32). Furthermore, landscape architectural and bioengineering strategies, such as vegetative planting and long-term monitoring, are essential for ensuring project success (Natural Resources Conservation Service 2018, 4-5).
By addressing both ecological and socioeconomic factors, the proposed design strategy aims to foster more resilient and sustainable landscapes. The project hypothesizes that the negative ecological impacts of Kiawe can be mitigated by repurposing its wood for practical applications like erosion control and site elements. In doing so, a problem may be transformed into a resource. That being said, the primary goal is to demonstrate how invasive species can be converted into valuable resources. This will involve gaining practical knowledge on the use of invasive species in ecological restoration for coastal sand dunes, addressing challenges for managing Kiawe stands, and finding alternative native species to replace Kiawe. The project will target specific sites in Hawai‘i where sand erosion is a significant issue, particularly dry coastal areas where Kiawe growth impacts groundwater discharge.
Methodology
This project will combine historical research, precedent analysis, literature review, site analysis, and experimental prototyping to investigate the potential for using Kiawe wood for coastal dune stabilization and construction materials for public parks on the island of Moloka‘i.
Historical Research
The project will examine the introduction and spread of Kiawe, its historical uses, and relevant indigenous practices. This will involve examining primary sources such as historical reports from the Hawai‘i Agricultural Experiment Station, geological surveys from the United States Geological Survey, and relevant literature on how the Prosopis species have been utilized for structure, tools, food and other traditional practices inside and outside of Hawai‘i. This analysis will provide context for understanding how Kiawe became established and its role in the local ecosystem and economy.
Precedent Analysis
The Precedent Analysis will examine existing projects that have utilized woody materials for coastal control and stabilization. It will evaluate the feasibility, effectiveness, and limitations of using Kiawe biomaterial in an erosion control system, drawing on case studies of real-world projects. This will include identifying best practices and challenges associated with these projects. The section will also explore a precedent related to native plant restoration, where native species were introduced to vulnerable areas to facilitate the reestablishment of a healthy coastal sand dune ecosystem.
Literature Review
The literature review will examine the existing body of knowledge on Kiawe biology, ecology, and management. This review will analyze scientific articles, reports, and other relevant publications to understand Kiawe’s growth habits, impacts on water resources, interactions with native species, and the effectiveness of various control methods. This section will also investigate the properties of Kiawe wood, such as its strength and durability in woodworking, to assess its suitability for sand dune stabilization and as a construction material.
Site Analysis
Site analysis will be conducted at two sites that are part of a large sand dune system called Keonele on Moloka‘i. Coastal erosion and ecologcial affects of Kiawe will be observed at Mo‘momi Beach Preserve and culturally significant spaces impacted by Kiawe will be observed at Pāpōhaku Beach Park. On that note, the project will prioritize coastal areas that are vulnerable to sand erosion and areas that provide opportunity to enhace cultural practices. Both sites obeservations will include: (1) assessing the extent of Kiawe abundance and the impact on the surrounding area and (2) assessing the potential for intervention.
Experimental Prototyping
The practical use of Kiawe wood will be explored through the fabrication of sample materials and or the construction of full-scale site elements. The objective is to evaluate how this material can be integrated into landscape designs to enhance public open spaces and ecological function. This process will involve sourcing Kiawe wood logs and using shop tools to create prototypes that can inform design strategies for rural sites such as Pāpōhaku Beach Park. The fabrication will address challenges posed by Kiawe’s crooked form, drawing on knowledge from traditional uses and applying contemporary creative ideas. Through this hands-on approach, the project will provide a clear understanding of how Kiawe wood can be used to support local communites on the island of Moloka‘i.
Literature Review
Bentrup, Gary, J. Chris Hoag, Interagency Riparian/Wetland Plant Development Project, Hollis Allen, Forrest Berg, David Blew, Jim Cornwell, et al. 1998. Streambank Bioengineering: A Guide for Landowners and Land Managers in the Great Basin and Intermountain West. United States Department of Agriculture Natural Resources Conservation Service. https://www.engr.colostate.edu/~bbledsoe/CIVE413/Practical_ Streambank_Bioengineering_Guide.pdf.
This book offers a valuable perspective on landscape restoration that considers the interconnectedness of the entire watershed. It stresses that eroding stream banks are often symptoms of larger issues that require an understanding of the dynamic forces shaping riparian areas. The guide focuses on the importance of adopting an interdisciplinary approach to assess the diverse factors influencing stream health, including the impact of land management practices such as agriculture, grazing, forestry, and urbanization.
The guide recommends a multiscale inventory and assessment to evaluate geomorphic valley forms, identify land management problems, and conduct a thorough site analysis. It frames bioengineering techniques as a tool to stabilize streambanks, using both biological and mechanical elements to support long-term success. However, it stresses that these techniques are not a substitute for proper land management, monitoring, and maintenance.
Burns, Russell M., and Barbara H. Honkala. 1990. “Kiawe.” In Silvics of North America: Hardwoods, Agricultural Handbook 674, 2:583–86. United States Department of Agriculture Forest Service. https://www.srs. fs.usda.gov/pubs/misc/ag_654_vol2.pdf.
This chapter covers the taxonomy, origin, habitat, and life history of Kiawe. It details the species introduction to Hawai‘i from a single tree in 1828 by Father Alexis Bachelot and its subsequent spread. The text emphasizes Kiawe’s adaptability to dry coastal areas, tolerance of saline soils, and association with other species. It further discusses the plant’s reproductive cycle, seed production, seedling development, and the growth rates as well as yields under different environmental conditions. The source also addresses the genetic aspects of the species, particularly the occurrence of thornless varieties, and management strategies. Gallaher, Timothy, and Mark Merlin. 2010. “Biology and Impacts of Pacific Island Invasive Species. 6. Prosopis Pallida and Prosopis Juliflora (Algarroba, Mesquite, Kiawe) (Fabaceae).” Pacific Science 64 (4): 489–526. https://doi.org/10.2984/64.4.489.
This article provides an overview of Kiawe, detailing its dual nature as both a valuable resource
and an invasive threat. The article discusses the introduction of this species to various regions and its economic importance for products such as fuel, fodder, and honey. It also highlights Kiawe’s ecological impacts, including both positive aspects such as soil stabilization and negative aspects such as competition with native species. The authors emphasize that management decisions should consider both positive and negative ecological roles. They explore the effectiveness of various control methods, such as detailing the use of biological controls for managing Kiawe populations in Hawai‘i. The resource also notes the allelopathic properties of the Prosopis species and its ability to form monotypic stands. Little, Elbert L., and Roger G. Skolmen. 1989. “Kiawe, algarroba.” In Common Forest Trees of Hawaii: Native and Introduced, Agricultural Handbook 679, 150–52. United States Department of Agriculture Forest Service. https://archive.org/details/common-forest-trees-of-hawaii/page/150/mode/2up?q=kiaw.
This chapter describes Kiawe as a post-Cook introduction that has become one of the most common and useful trees in the dry lowlands of Hawai‘i. This resource provides detailed morphological information, noting that the tree is a small to medium-sized deciduous tree with a short, often crooked trunk and wide-spreading crown. It has bipinnate leaves with many small leaflets, and produces yellowish, bean-like pods. The wood of the Kiawe is very heavy and hard, making it useful for various purposes including charcoal, fuelwood, and fence posts. The pods are a valuable source of livestock feed and the flowers are an important nectar source for bees. Additionally, the tree produces large thorns that make walking beneath it hazardous.
Natural Resources Conservation Service. 2018. “Practice Specification Brush Management (Code 314).” United States Department of Agriculture. September 2018. Accessed January 31, 2025. https://efotg.sc.egov. usda.gov/api/CPSFile/6406/314_PI_PS_Brush_Management_2018.
This document outlines the technical requirements for managing brush, focusing on the control of woody species while preserving desired vegetation. It details various control methods, including biological, chemical, and mechanical approaches. A critical component of this specification is the requirement for a detailed brush management plan that is tailored to each specific project. This plan must consider a range of factors such as: land user objectives, site characteristics, topography, the growth habits of the target species, and the size and distribution of plants. Additionally, the plan must account for potential hazards, costs, and the existing or potential for erosion. The document highlights Kiawe as a common target species in the Pacific Islands Area. Since Kiawe is a known root-sprouter, multiple treatments or a combination of treatments are often necessary for effective control. Furthermore, the brush management plan must document revegetation needs, which should be implemented as soon as possible after clearing, ideally at the start of the rainy season. The document underscores that careful planning, selection of appropriate treatment methods, and consistent follow-up maintenance are essential for successful management of Kiawe in Hawai‘i. Pongkijvorasin, Sittidaj, Kimberly Burnett, and Christopher Wada. 2017. “Joint Management of an Interconnected Coastal Aquifer and Invasive Tree.” Ecological Economics 146 (October): 125–35. https://doi.org/10.1016/j. ecolecon.2017.10.011.
This article examines the economic impact of Kiawe on groundwater resources, specifically focusing on the tree’s transpiration rates. The study highlights that kiawe, a phreatophyte or “groundwater-loving plant,” possesses a root system capable of accessing deep groundwater sources. In the Kīholo Bay area on Hawai‘i Island, Kiawe was found to transpire significantly more water than was supplied via rainfall, with annual transpiration rates estimated to be roughly 84% higher than rainfall.
This high transpiration rate, with a baseline uptake value of 1.6 tm3/ha/year, results in a negative water budget for the study site due to groundwater uptake and continuous transpiration by Kiawe. The study emphasizes that an efficient joint management strategy must recognize the links between water and invasive species. Further noting that managing invasive species can affect water quality and that the economic damage caused by Kiawe is not linear with water demand growth.
The study finds that the decision to remove Kiawe depends on water demand and removal costs. If water demand is projected to grow at least 2% per year, removing all Kiawe is optimal. Moreover, the economic damages of Kiawe remain low until water demand growth is about 1.45%. Once this rate is
exceeded, damages increase rapidly. This means that even small differences in projected water demand growth rates can have large effects on the economic justification for Kiawe removal. Simpson, B.B. 1977. “Mesquite in Indian Cultures of Southwestern North America.” In Mesquite, Its Biology in Two Desert Scrub Ecosystems, US/IBP Synthesis Series, 4:150–76. Dowden, Hutchinson & Ross Inc. https:// archive. org/details/mesquiteitsbiolo0000unse.
The author demonstrates that Mesquite was not just a plant, but a vital resource serving multiple purposes. It provided food, fuel, shelter, tools, weapons, fibers, and medicine. Beyond its practical applications, the text also explores the cultural significance of Mesquite, its role in religious and ritualistic practices, and its deep connection to indigenous people in desert environments. By detailing harvesting and preparation techniques, the chapter sheds light on the complex relationship between the people and Mesquite. That being said, this source provides valuable insight into indigenous knowledge and traditional practices related to Mesquite, serving as a comparative reference for exploring whether similar practices could be applied to Kiawe (Hawaiian Mesquite) in Hawai‘i.
Narrative
Prosopis pallida, commonly known as Kiawe, was first introduced to Hawai‘i in 1828 when Father Alexis Bachelot planted seeds in Honolulu (Little and Skolmen 1989, 152; Gallaher and Merlin 2010, 504). Though originally believed to have come from France, the seeds were more likely sourced from South America (Gallaher and Merlin 2010, 504). By 1840, Kiawe had become a popular shade tree in Honolulu, and it has since spread across more than 150,000 acres in the Hawaiian Islands (Burns and Honkala 1990, 583). It has become widespread in Hawai‘i’s dry lowlands and is classified as invasive (Little and Skolmen 1989, 150; Gallaher and Merlin 2010, 489).
Kiawe thrives in arid environments and is capable of growing in diverse substrates, including saline and alkaline soils, coastal sands, and old lava flows (Little and Skolmen 1989, 150, 152; Gallaher and Merlin 2010, 504). Its deep taproot system enables access to groundwater far below the surface, which contributes to high rates of transpiration and the potential depletion of local water tables (Gallaher and Merlin 2010, 491; Pongkijvorasin et al. 2017, 125–126). In already water-scarce environments, this trait can alter local hydrology and limit water availability for native plant species and human use (Pongkijvorasin et al. 2017, 125–126).
In addition to its hydrological impacts, Kiawe forms dense, thorny thickets that displace native vegetation and degrade habitat quality (Gallaher and Merlin 2010, 494–495, 500). This displacement is particularly problematic in sensitive coastal dune ecosystems like those at Mo‘omomi Beach Nature Preserve, where native plant cover is critical for stabilizing sand dunes and supporting endemic species.
Despite its invasive characteristics, Kiawe also presents opportunities for resource use and landscape adaptation. Its dense hardwood is prized as a fuel source, commonly used for firewood and charcoal. However, the tree also supports honey production through its nectar, while its seed pods are used as cattle fodder (Little and Skolmen 1989, 150; Burns and Honkala 1990, 585; Gallaher and Merlin 2010, 496–498). Additionally, the heartwood is rot-resistant and valued for fence posts and small-scale woodcrafts (Honkala 1990, 585; Little and Skolmen 1989, 150).
The presence of Kiawe in Hawai‘i represents a dual reality: an ecological challenge and a potential material resource. As a phreatophyte, Kiawe consumes substantial groundwater, contributing to a negative water budget in dry regions and placing stress on already limited water supplies (Pongkijvorasin et al. 2017, 125–126). Its ecological impacts, particularly in areas like Moloka‘i, necessitate adaptive management strategies that go beyond eradication. Research suggests that complete removal of Kiawe may be economically viable if water demand continues to increase by at least 2% annually and removal costs remain manageable (Pongkijvorasin et al. 2017, 132).
This capstone project seeks to reframe the issue: rather than focusing solely on Kiawe’s removal, it explores how the tree’s physical and structural properties can be repurposed. By using Kiawe wood in the construction of coastal dune stabilization structures at Mo‘omomi Beach and landscape elements at Pāpōhaku Beach Park, this project aims to transform a persistent invasive species into a material resource, supporting both ecological restoration and cultural engagement.
This capstone project examines the introduction of Kiawe (Prosopis pallida) to Hawai‘i and explores its potential to be repurposed from an invasive species into a valuable resource. Centered on Moloka‘i, it evaluates two key applications of Kiawe wood:
(1) Coastal dune stabilization structures at Mo‘omomi Beach Nature Preserve
(2) Construction materials for use at Pāpōhaku Beach Park
The goal is to transform an ecological problem into a resource.
Research Questions
1. What ecological and historical factors have contributed to the proliferation of Kiawe as an invasive species in Hawai‘i?
2. What are the ecological impacts of Kiawe on coastal dune ecosystems, specifically at Mo‘omomi Beach Nature Preserve?
3. What types of coastal dune stabilization structures can be constructed using Kiawe to promote dune formation and resilience at Mo‘omomi Beach Nature Preserve?
4. Which native plant species are most suitable for replacing Kiawe monocultures at Pāpōhaku Beach Park, and how can they support cultural practices?
5. What landscape elements can be designed using Kiawe wood at Pāpōhaku Beach Park to support park vibrancy and recreation?
Species Overview
Family
Fabaceae
Genus
Prosopis
Species
Pallida
Common Name(s)
Kiawe, Algaroba, Mesquite
Hawaii Weed Risk Assessment
Score: 20 (Plant Pono 2021).
High Risk
The image above depicts Prosopis pallida emerging from pāhoehoe lava in North Kona, Hawai‘i (Gallaher and Merlin 2010, 502). Unlike many native and introduced species, Kiawe demonstrates a remarkable capacity to establish itself in some of the most inhospitable environments of the Hawaiian Islands. This ecological resilience has enabled it to become widespread across dry lowlands and barren terrain.
02 History
Reviewing
Kiawe’s arrival and spread throughout the Hawaiian Islands
Father Bachelot’s kiawe tree planted in Honolulu, Hawaii around 1902.
Photo Credit: Reginald Yzendoorn
Honolulu, Hawai‘i
Photo Credit: Diocese of Honolulu Archives
Arrival in Hawai’i
Kiawe, or Prosopis pallida, is a thorny tree that has become widespread in Hawai‘i’s dry forests after escaping cultivation (Plant Pono 2021). Native to Peru, Colombia, and Ecuador, its introduction to Hawai‘i began with a single seed brought in 1827 by Father Alexis Bachelot (1796–1837), the first Catholic priest in the Hawaiian Islands (Gallaher and Merlin 2010, 504). The seed was reportedly collected from a tree in the Jardin du Roi in Paris and transported aboard the French ship La Comète (504). However, since the Comète stopped in Lima and Arequipa, Peru, before arriving in Hawai‘i, these locations may have been the true source of the seed (504).
Another account notes that after departing France in November 1826, the missionaries arrived in Valparaíso, Chile, on February 8, 1827, staying two weeks before continuing to Hawai‘i (Louis 2019). Experts believe the Kiawe species in Hawai‘i is native to northern Chile and southern Peru. Originally misclassified as Prosopis chilensis, it was later reidentified as Prosopis pallida following further taxonomic study (Gallaher and Merlin 2010, 490).
The first Kiawe tree grew in the churchyard of the Cathedral of Our Lady of Peace on Fort Street, Honolulu. By August 1832, it was bearing fruit (Gallaher and Merlin 2010, 504; Burns and Honkala 1990, 583). By 1840, Kiawe had become Honolulu’s main source of shade, thriving in the city’s hot, dry climate where other species struggled (Little and Skolmen 1989, 152; Plant Pono 2021). Prior to its introduction, Honolulu had few trees, making Kiawe a vital addition to the urban landscape by the early 1900s (Little and Skolmen 1989, 152).
The original tree eventually reached a diameter of about 1 meter (approximately 3.2 feet) and was cut down on October 23, 1919, at the age of 91 to make way for the Knights of Columbus building on Fort Street (Gallaher and Merlin 2010, 507; Louis 2019). A 15-foot trunk section was preserved in the cathedral courtyard to commemorate it (Louis 2019). Over time, it was gradually reduced by souvenir hunters and only a stump remains today, marked by a plaque describing its historical significance (Louis 2019).
Kiawe’s Route to the Hawaiian Islands
The progeny of the original Kiawe tree spread across the dry, leeward plains of all the main Hawaiian Islands (Plant Pono 2021; Burns and Honkala 1990, 583). By 1916, Kiawe covered an estimated 32,000 hectares (79,072 acres) in Hawai‘i (Gallaher and Merlin 2010, 507). Leeward belts of Kiawe forest extended from near the shoreline to elevations of 250–300 meters (280–984 feet) on all major islands (507). Remnants of over 12,000 hectares (approximately 29,653 acres) remain around the developments and suburbs of leeward O‘ahu (504). Large stands are still found on Hawai‘i Island, Moloka‘i, and Ni‘ihau, where cattle ranching persists and development is limited (504).
The species has also spread beyond Hawai‘i. In the Marquesas Islands, it was introduced before 1964 to at least two locations on Ua Huka (Gallaher and Merlin 2010, 499, 506). Similar specimens have been observed in the Galápagos Islands, though it remains unclear whether they are native or introduced (499).
In Australia, Kiawe was the first of four Prosopis species introduced, beginning with a single tree planted in the Brisbane Botanical Gardens in the 1880s. This tree was likely from seeds imported from Hawai‘i (Gallaher and Merlin 2010, 508). Today, widespread populations in Western Australia and Queensland also likely trace their origins to Hawaiian material (508).
According to Burns and Honkala (1990), seeds were shipped from Hawai‘i to Cuba, Arabia, Australia, Fiji, and South Africa as early as 1937 for the purpose of breeding thornless varieties (585–586). However, these efforts were often unsuccessful, further contributing to the species’ spread (586). Additional recorded introductions from Hawai‘i include Bahrain (1920–1930), China (1815), and Kenya (1973) (Gallaher and Merlin 2010, 506).
The spread of Prosopis pallida from Hawai‘i to other dry regions demonstrates its adaptability, but also the ecological risks of introducing species without fully understanding their long-term impacts. Kiawe’s global reach serves as a reminder of how quickly usefulness can turn into invasiveness, offering a cautionary example of human influence on fragile ecosystems.
03 Anatomy
Examining the morphology and defining features of Kiawe
A seed pod desiccating naturally after detachment from a kiawe tree in Waianae, Oahu.
Physical Characteristics
The following information about the plant anatomy of Prosopis pallida (Kiawe) is adapted and paraphrased from the research of Little & Skolmen (1989):
Tree Form
Kiawe is characterized by a short, irregular trunk supporting a broad, asymmetrical crown. Its narrow, bean-shaped pods, which appear slightly yellowish from a distance, provide a subtle contrast against the surrounding green foliage.
Bark, Trunk, Twigs
The trunk of the tree is typically crooked, twisted, fluted, and angled, with widely forking branches. The bark is finely fissured, with a gray-brown outer layer and an orange-brown inner layer. Twigs are green, smooth, and slightly zigzagged in appearance. At the base of the leaves, they commonly bear one or two spreading thorns, which may reach up to 2.5 cm (1 inch) in length.
Leaves
Leaves are alternately arranged on long twigs and are generally light green, with fine hairs along their surfaces. They are bipinnate and usually measure 7.5 cm (3 inches) or less in total length. Each leaf consists of a short central axis, typically under 2.5 cm (1 inch), with two to three pairs of side axes, each 2.5–4 cm (1–1.5 inches) long. Glandular dots appear between the side pairs. The leaflets are small and numerous, arranged in 8 to 11 pairs. They are stalkless, narrowly oblong, approximately 6 mm (1/4 inch) long and less than 3 mm (1/8 inch) wide, with rounded tips and asymmetrical bases. Their texture is thin and delicate.
Flower
Kiawe flowers are borne in lateral, drooping spikes that measure 7.5–10 cm (3–4 inches) in length and about 1.5 cm (5/8 inch) in width. These unbranched clusters contain numerous, densely packed, light yellow flowers, each about 6 mm (1/4 inch) long. Every flower includes a green, cuplike calyx with five teeth, a corolla of five narrow petals, ten threadlike stamens, and a slender pistil with a hairy ovary, curved style, and dotted stigma. Flowering primarily occurs during the spring and summer months.
Fruit
The fruits are bean-like pods, few in number, and suspended on slender stalks. They are yellowish, narrow, and slightly flattened, ranging from 7.5–20 cm (3–8 inches) in length, 1 cm (3/8 inch) in width, and approximately 5 mm (3/16 inch) in thickness. Each pod is pointed at both ends and remains closed at maturity. Inside, the pod contains a mildly sweet, whitish pulp that surrounds 10 to 20 seeds. These seeds are enclosed in a four-angled whitish covering. They are elliptical, slightly flattened, about 6 mm (1/4 inch) long, and have a shiny light brown appearance.
Wood
Kiawe wood is dark reddish-brown, extremely hard, and dense, with a specific gravity of 0.85. It exhibits minimal shrinkage when dried and the heartwood is highly resistant to decay, although somewhat susceptible to marine borers. Additionally, the bark contains tannin and produces a brownish gum.
Botanical Plate
Prosopis pallida, Kiawe
e.
e.
f.
g.
c. d.
a. calyx and ovary, b. flower, c. leaf, d. thorn,
seed, f. mature pod, g. young pod
Developmental Traits
Growth Forms
Kiawe is remarkably adaptable in form, shaped by the environments it inhabits. In favorable conditions, it can grow into a tall, straight-trunked tree over 20 meters (66 feet) tall and 1 meter (3 feet) wide (Gallaher and Merlin 2010, 491). In harsher settings, such as dry, windswept coastal areas, it often takes a shrubby, twisted form just 3 to 5 meters (10–16 feet) tall (Burns and Honkala 1990, 585). These growth forms are shaped by factors like wind, salt spray, drought, grazing, or repeated cutting (Gallaher and Merlin 2010, 491). While Kiawe may thrive and grow large with abundant moisture, these same conditions can lead to shallow root development and increased vulnerability to windthrow (Burns and Honkala 1990, 585). Conversely, in drier areas with harsher conditions, its smaller forms dominate, hugging the ground in places where few other trees persist.
Reproductive Strategies
Kiawe reproduces both by seed and vegetatively, making it especially persistent and quick to spread. In Hawai‘i, flowering begins as early as three to four years of age and can occur throughout the year, with peaks between January and March, and often again in the fall following wet summers (Burns and Honkala 1990, 584). Pollinated by insects, its flowers make Kiawe a valuable honey plant. Germination is epigeal, and seeds sprout most successfully after passing through the digestive tracts of livestock, which is a trait that helped accelerate its spread across grazed lands in Hawai‘i (Gallaher and Merlin 2010, 504). In moist, open areas, seedlings may grow over a meter tall in their first year, but survival depends on sufficient early rainfall, and they are intolerant of shade (Burns and Honkala 1990, 584).
Vegetative regrowth adds another layer to its resilience. Stumps resprout readily after cutting, often requiring follow-up management within six months to two years (Natural Resources Conservation Service 2018, 4). While thornless varieties have been experimentally propagated by air layering and misted cuttings, stump sprouting remains the primary regeneration method after disturbance (Burns and Honkala 1990, 584). This trait complicates removal efforts and makes Kiawe difficult to eliminate once established.
Root Systems and Water Use
Kiawe’s root system plays a central role in its success in arid environments. As a phreatophyte, it develops a deep taproot capable of reaching groundwater, while its lateral roots capture moisture from surface rain events (Burns and Honkala 1990, 585; Pongkijvorasin et al. 2017, 125). This dual strategy enables it to survive drought conditions and outcompete other species. However, Kiawe’s water use is not without consequence. Research on Kaho‘olawe has linked its expansion to declines in local groundwater levels (Pongkijvorasin et al. 2017, 125; Gallaher and Merlin 2010, 495). Internally, Kiawe efficiently redistributes water throughout its tissues, allowing it to remain productive even under dry conditions (Gallaher and Merlin 2010, 509).
When conditions are ideal, Kiawe grows rapidly, reaching heights of 6 to 8 meters (20–26 feet) in just a few years (Pongkijvorasin et al. 2017, 125). However, it is highly intolerant of shade and is often outcompeted in wetter, forested environments (Burns and Honkala 1990, 585). In the sunny, dry coastal lowlands of the Hawaiian Islands, Kiawe thrives with little competition, further fueling its long-term dominance over native species.
Refer to diagram on page 22.
Tap Root
Lateral Root
Root Types
Fiberous Roots
Allelopathic Properties
Gallaher and Merlin (2010) highlight the presence of allelopathic substances in the leaves of Prosopis juliflora, a species closely related to Prosopis pallida, commonly known in Hawai‘i as Long-thorn Kiawe (490, 494). While they do not explicitly state that P. pallida shares these allelopathic properties, the ecological similarities between the two species and their overlapping roles suggest that the findings regarding P. juliflora may be relevant when considering potential allelopathic effects in Hawai‘i.
The researchers found that leachate from P. juliflora leaves contains several allelopathic compounds, including L-tryptophan, syringim, and ()-lariciresinol, which are released through water spraying (Gallaher and Merlin 2010, 494, 522). Further studies have identified alkaloids in leaf extracts that inhibit plant growth (494). These substances may negatively affect the germination and growth of species that would typically establish beneath the canopy of Kiawe trees. This could help explain the displacement of native vegetation in Hawai‘i’s dry leeward areas, especially following the spread of Prosopis species (Gallaher and Merlin 2010, 494; Miyazawa et al. 2015, 1167). While human activities, such as browsing by introduced ungulates and frequent burning, are primarily responsible for the initial decline in native plants, the continued dominance of Kiawe may restrict the regeneration of these species, potentially due in part to allelopathy (Gallaher and Merlin 2010, 494).
Although the research specifically identifies these allelopathic substances in P. juliflora, it is important to consider that P. pallida, which shares similar ecological traits and invasive behaviors, might also exhibit allelopathic effects. As Gallaher and Merlin (2010) note, further research is needed to investigate how Kiawe interacts with other plants, particularly in Hawai‘i’s dry ecosystems, where dense, monotypic stands could significantly shape plant community dynamics (515). The diagram on page 26 illustrates the native plant species that compete with Kiawe in the same ecological zone.
Native Plant Palette for Coastal to Mesic Lowlands
‘A’ali’i Dondonaea viscossa
‘Akulikuli Sesivium portulacastrum
‘Ilie’e Plumbago zeylanica
Milo Thespesia moluccana
‘Ohai Sesbania tomentosa
Pua Kala Argemone glauca
‘Aki’aki Sporobolus virginicus
Hala Pandanus tectorius
Kolomona Senna gaudichaudii
Naio Myoporum sandwicense
‘Ākia Dondonaea viscossa
Hinahina Kahakai Heliotropium Anomalium
MaiapiloCapparis sandwichiana
Nanea Vigna marina
Pā’ū o Hi’iaka Dondonaea viscossa Pōhinahina Vitex rotundifolia
Highlighting the material significance and cultural applications of Kiawe in and beyond Hawai’i
An open-air structure with a kiawe wood frame and palm frond roof at Pāpōhaku Beach, Moloka’i.
Traditional Uses
Both Kiawe (Prosopis pallida) and its closely related species, Mesquite (Prosopis glandulosa), have been important to Indigenous groups from precolonial times to the present, particularly for medicinal purposes. The leaves and gum of Mesquite were commonly used to treat eye ailments. For example, the Aztecs combined Mesquite leaves and gum to relieve eye pain and inflammation (Simpson 1977, 166). Similarly, the Mescalero Apache and other groups in Baja California ground the leaves into powder, wrapped it in cloth, and applied the resulting liquid to affected eyes, while the Paipai and Pima boiled Mesquite leaves to create a solution for washing inflamed eyes (166). Mesquite gum dissolved in water was also used as a remedy for sore throats, with the Pima preparing hot tea from the sap (166–67).
Beyond medicinal uses, Mesquite wood was crafted into a variety of tools and weapons, including planting sticks, digging tools, and trays, as well as war clubs and fending sticks (166–67, 172). The Seri people made extensive use of Mesquite, using thorns for sewing and roots for making strong cordage (170, 172). After softening the fibers by chewing, they twisted the roots into twine or rope, which was essential for binding harpoon points and creating harpoon lines (170).
Root with bark removed, pounded, and doublestranded into twine (Simpson 1977, 171).
Mesquite cordage was also used by the Seri to tie reedgrass for constructing balsas, seagoing reed boats that could measure up to 33 feet in length (171). They also built temporary rafts from driftwood for sea turtle hunting, which they dismantled after use to preserve the valuable material (171).
The Kamia made twine from the inner bark of Mesquite, soaking it for a month before spinning it on their thighs (171). The Cocopa and Mohave also used mesquite roots and bark in basketry (162).
The diverse and multifunctional uses of Prosopis highlight its historical significance as a versatile resource in the cultural practices of communities across arid regions. These traditional methods of construction and medicine have evolved over time to meet the changing needs of civilizations.
Key Materials
The following are contemporary materials derived from the Prosopis species:
Wood
The timber is valued for its durability, strength, hardness, and resistance to rot (Gallaher and Merlin 2010, 498). It can be processed into a variety of products, including boards, cants, furniture, parquet flooring, and tool handles (Pasiecznik et al. 2001, 80).
Pulp
The wood can be pulped to produce textile fibers, tire cord, cellophane, and writing or printing papers (Pasiecznik et al. 2001, 81).
Flour
Pulp flour is used as an ingredient in various food products, such as cakes, ice creams, and desserts. It also serves as a sugar substitute, reducing the need for added sweeteners (Pasiecznik et al. 2001, 91).
Pods
The pods’ high sugar content can be converted into liquid fuel, offering potential as a biofuel source through the processing of carbohydrates into ethanol (Gallaher and Merlin 2010, 497).
Gum
The gum produced by the pods and bark can be used as an emulsifier and thickening agent in adhesives and pharmaceuticals (Gallaher and Merlin 2010, 498).
Tannins
Tannins extracted from the bark, wood, and fruit have been used to treat animal hides (Gallaher and Merlin 2010, 498). They are also used in the production of black dye for ink preparation (Pasiecznik et al. 2001, 99).
Timeline of Applications in Hawai’i
Honeybees were introduced to Hawai‘i (Little and Skolmen 1989, 150).
Kiawe was recognized as a valuable cattle feed and fuelwood source (Gallaher and Merlin 2010, 504).
Kiawe dominated dry, lowland areas on O‘ahu, and its wood was sold commercially in Honolulu for $9–$10 per cord for use as fence posts and fuel (Gallaher and Merlin 2010, 504).
Kiawe flowers were recognized as a significant nectar source, promting large scale planting operations. The honey industry reached a value of $100,000 (Gallaher and Merlin 2010, 504).
Recommendations were made to reforest lowland areas with Kiawe, particularly on Kaho‘olawe (Gallaher and Merlin 2010, 507).
At it’s peak, Hawai‘i exported 1,000 tons of Kiawe honey (Gallaher and Merlin 2010, 506).
The Hawai‘i Agriculture Experiment Station developed a seed grinding process, which lead to the creation of a $400,000 cattle feed industry (Gallaher and Merlin 2010, 506).
An estimated 79,072 acres of Kiawe spread across the Hawaiian Islands, and pod collection became a notable economic activity (Gallaher and Merlin 2010, 506).
A decline in O‘ahu’s cattle industry later reduced the spread of Kiawe (Gallaher and Merlin 2010, 507).
The American Sugar Company on Moloka‘i became the world’s largest honey producer, producing 500,000 pounds of honey (Eckert and Bess 1952, 5).
Kiawe populations declined significantly on O‘ahu, while active recruitment and spread continued on the outer islands (Gallaher and Merlin 2010, 514).
Kiawe remains important for charcoal, honey, fuelwood, fence posts and imu construction in areas with abundant stands, especially on Moloka‘i (Gallaher and Merlin 2010, 508).
Imu
(earth oven) on Kaho’olawe heated with Kiawe wood (Riley et al. 2019, 117).
Advertisement for Kiawe bean feed for horses and cattle in 1913–1920 (Gallaher and Merlin 2010, 504).
Kiawe charcoal bag from Maui sold commercially in Hawai’i (Gallaher and Merlin 2010, 504).
Honeybee apiary on Moloka‘i surrounded by a Kiawe grove (Eckert and Bess 1952, cover).
05 Site Analysis
Locating Kiawe abundance in the coastal dune landscape of Moloka’i
Kiawe thickets encroach on the sandy shoreline, competing with native ‘aki‘aki (seashore rushgrass) at Pāpōhaku Beach, Moloka’i.
Overview and Findings
The following maps provide contextual analysis to explain how Pāpōhaku Beach Park and Mo‘omomi Beach Preserve were selected as the primary focus areas for this project. Each layer of spatial data reveals critical environmental and cultural conditions that inform the opportunities associated with Kiawe management.
Average Rainfall
- (1”=15,000’)
The rainfall map highlights West Moloka‘i as an arid region, receiving only 8 to 30 inches of rain annually. This low-precipitation zone supports the widespread growth of Kiawe, a species well-adapted to dry environments where many native plants struggle to survive.
Ahupua‘a Land Boundaries and Streams
- (1”=15,000’)
This map illustrates traditional land divisions (ahupua‘a and moku) and compares the distribution of surface water across the island. West Moloka‘i contains significantly fewer streams than East Moloka‘i, reinforcing the idea that the western region has more limited freshwater resources. This lack of surface water further favors the establishment of drought-tolerant species like Kiawe.
Geology
- (1”=15,000’)
The geology map identifies locations of sand dune formations and deposits. Of particular importance are two sites that were once part of a single dune system on West Moloka‘i: Mo‘omomi Beach to the northwest and Pāpōhaku Beach to the west. Their geological composition and alignment suggest a unique relationship in dune formation and wind-driven sand transport.
Land Cover -
(1”=7,500’)
Land cover analysis shows that the area between the two sites is predominantly classified as herbaceous and mixed rangeland. These open landscapes are sparsely vegetated, with few trees, allowing Kiawe to dominate in the absence of significant vegetative competition.
Land Ownership -
(1”=5,000’)
This map outlines property boundaries and identifies potential sites for public design interventions. A significant portion of West Moloka‘i is privately owned by Moloka‘i Ranch, which holds approximately 53,000 acres island-wide. The two primary project sites, Pāpōhaku Beach Park (City and County of Maui) and Mo‘omomi Nature Preserve (The Nature Conservancy), represent public and private holding. Respectively, both are aligned with conservation and public use values.
100’ Contours & Wind Direction -
(1”=5,000’)
Topography and wind pattern data are key to understanding the spatial dynamics between the two beaches. The prevailing northeast trade winds transported sand from Mo‘omomi Beach Preserve over ridge lines reaching elevations up to 600 feet, ultimately depositing material at Pāpōhaku Beach. The absence of a fringing reef in front of Pāpōhaku limits local coral sedimentation, which otherwise contributes to beach formation. This geological and atmospheric interaction created what was once the largest sand dune ecosystem in Hawai‘i, historically known as Keonelele, or “the flying sands.”
Historical Sand Mining 1950 & 1964 - (1”=3,500’)
Two historical aerial maps provide insight into anthropogenic changes along Pāpōhaku Beach. In 1950, Kaupoa Road did not exist. By 1964, it was constructed to connect the beach’s southern end to Hale o Lono Harbor to the south. This road facilitated large-scale sand extraction operations that transported sand from Pāpōhaku to Waikīkī Beach on O‘ahu, contributing to the depletion of the native dune system.
Pāpōhaku Beach
Site of HC&D Sand Mining Operations
Sand erosion still occurs in adjacent areas due to seasonal swell and wind changes
Mining operations, combined with natural erosion, have exposed bare sandstone
A revetment was installed to mitigate coastal erosion at the site of previous sand mining activity
06 Mo‘omomi
Developing management strategies to support dune growth at Mo’omomi Beach Preserve using Kiawe
biomaterial
A coastal sand dune trail featuring native beach naupaka and aki’aki’ grass at Mo’omomi Beach, Moloka’i.
Photo Credit: Noah Lang
Sand erosion is also a concern at this site, though not to the extent seen at Pāpōhaku Beach
Removing Kiawe thickets near the shoreline can destabilize areas where native species are struggling to regenerate naturally
Photo Credit: Noah Lang
Photo Credit: Noah Lang
A predator fence was installed to protect the area from damage caused by invasive species, particularly axis deer...
Photo Credit: Noah Lang
Predator Staging Area
On September 26, 1999, a wedge-tailed shearwater nest was observed on the eastern end of Mo‘omomi Preserve (The Nature Conservancy 2017, 19). Following this discovery, The Nature Conservancy initiated ongoing predator control efforts to safeguard the native seabird population. Paired with habitat restoration through Kiawe removal, these actions have resulted in the establishment of over 1,400 wedgetailed shearwater nests in the preserve today (12).
Kiawe thickets act as staging areas for predators such as feral cats, dogs, and mongoose, which pose a significant threat to the shearwater
population (14). These dense, invasive stands provide cover, allowing predators to approach nests undetected and increasing the risk of predation. Additionally, axis deer disturb nesting sites by trampling vegetation and crushing eggs, further threatening the fragile coastal ecosystem (12). These thickets also create a fire hazard and hinder natural habitat restoration (14). To mitigate these challenges, The Nature Conservancy installed a 1.5–mile fence in 2016 to exclude both deer and predators from critical seabird habitats (12). Combined with continued kiawe removal and habitat restoration efforts, these measures support the protection and recovery of the native seabird population.
Management Response
The Nature Conservancy (2017) prioritizes the removal of smaller, fragmented, and isolated stands of Kiawe, particularly those located in areas with high salt spray exposure and in proximity to native vegetation (14). Crews cut the stands in lines perpendicular to the prevailing trade winds and treat the stumps with herbicide to prevent regrowth. The felled wood is chipped to reduce biomass, and the resulting material is distributed across the removal area as mulch (15).
According to the Long Range Management Plan 2014–2019, approximately 11 acres of Kiawe have been removed within the fenced area of the preserve,
with an estimated 60 acres remaining (The Nature Conservancy 2017, 16). The Nature Conservancy emphasizes that Kiawe removal will remain a management priority, and staff are instructed to notify the Moloka‘i subcommittee of the Maui Invasive Species Committee (MoMISC) should any new invasive weed species be identified near the preserve (16).
Post-removal, invasive grasses and weeds are routinely managed to prevent the development of an invasive seed bank, thereby allowing native vegetation to regenerate passively (8). When funding permits, outplanting of native species is conducted to supplement natural recovery processes (15).
Based on monitoring of regeneration rates, weed pressure, and funding availability, a realistic
target for Kiawe removal has been set at 0.20 acres per year (15).
Proposed Management Strategy
This capstone project proposes an enhancement to the existing Kiawe removal strategy by repurposing the felled biomass into temporary sand dune stabilization structures. While invasive, Kiawe currently contributes to dune stability in areas where native vegetation has not yet reestablished. Upon removal, these dunes can become destabilized, especially given the slow growth rates of some native species and the limited capacity for outplanting due to financial constraints.
The proposed structures, built from harvested
Kiawe wood, aim to reduce erosion and foster sand accumulation in restoration zones. They would serve as transitional buffers, supporting native plant establishment. This approach bridges the ecological gap between invasive removal and full native restoration, enhancing long-term outcomes while allowing time to secure funding and implement further restoration activities.
Stake Thatching Precedent Study
Location: Ballston Beach, Cape Cod, Massachusetts
Strategy: Wind-driven sand accumulation using stake matrices
A compelling precedent for natural dune stabilization can be found at Ballston Beach in Cape Cod, Massachusetts. As documented by Safe Harbor (2024), the technique, known as “stake thatching,” was developed to simulate the function of coastal vegetation in capturing wind-blown sand and reinforcing dune systems.
The project involved inserting 14-inch cedar stakes a few inches into the sand in a randomized grid, spaced 10 to 14 inches apart and arranged in 4 to 6-foot-wide bands along the upper beach. Over 26 months, this intervention facilitated the accumulation of 22 to 24 vertical feet of new sand.
As sand levels increased, the stakes were progressively raised to remain effective. This low-tech, adaptive strategy demonstrates the potential for similar applications using Kiawe wood in coastal restoration efforts on northern shorelines across Hawai‘i.
Photo Credit: Safe Harbor
Photo Credit: Safe Harbor
Post & Brush Clustering Precedent Study
Location: Diogué Island, Senegal, Africa
Strategy: Tidal sand accumulation using semi-permeable brush structures
On Diogué Island in Senegal, a coastal restoration technique known as post and brush clustering has proven effective in promoting sand accumulation through tidal processes. As described in Simple Ways to Fend Off Coastal Erosion (2022), this method involves constructing clusters of wooden posts interwoven with palm fronds and other biodegradable materials. These structures are arranged with side arms oriented at 45 to 90–degree angles to the shoreline, allowing them to trap sediment as waves move inland. Unlike rigid infrastructure such as stone or concrete, the semi-permeable design reduces the risk of disrupting nearshore currents or triggering erosion in adjacent areas.
O ver a three-year period, a 1.5–kilometer (0.93–mile) beach gained up to 30 meters (98 feet) of new sand. The use of organic, low-impact materials in this strategy presents valuable possibilities for adapting Kiawe biomass in shoreline restoration projects along moderate to low-energy coasts in the Hawaiian Islands.
Photo Credit: Reuters
Photo Credit: Reuters
Log Trapping Precedent Study
Location: Popham Beach Park, Phippsburg, Maine
Strategy: Wind-driven sand accumulation using log barriers
At Popham Beach Park in Phippsburg, Maine, a nature-based approach to dune restoration was implemented using storm-washed logs and discarded Christmas trees to encourage wind-driven sand accumulation. As reported by the NOAA Office for Coastal Management (2024), the materials were strategically placed parallel to the shoreline to simulate natural dune ridges.
This configuration facilitated the rapid accumulation of sand, with visible results occurring within just one week. Over the following four months, inland logs continued to trap sediment and provided a stable substrate for dune grass regeneration. Despite some exposure to shoreline washout, the system demonstrated resilience under low to moderate-energy coastal conditions.
This precedent suggests that repurposed organic debris, including Kiawe logs, could serve as an effective material for similar dune-building interventions in Hawai‘i, especially where native vegetation is slow to establish or restoration resources are limited.
Photo Credit: NOAA Office for Coastal Management
Photo Credit: NOAA Office for Coastal Management
Photo Credit: NOAA Office for Coastal Management
Post Fencing Precedent Study
Location: Kanahā Beach Park, Maui, Hawai‘i
Strategy: Wind-driven sand accumulation using log barriers
At Kanahā Beach Park on the island of Maui, post fencing has been utilized as a rapid intervention strategy to promote sand accumulation in response to coastal erosion. As documented by the University of Hawai‘i Sea Grant and partners (2022), this technique involves the installation of wooden slats or panel fencing oriented at 45 to 90–degree angles to prevailing winds.
These structures are designed to intercept wind-blown sand and encourage the formation of low dune features. While effective in initiating short-term dune growth, particularly in emergency situations, the method proved less suitable for narrow or high-energy beaches. Additionally, frequent maintenance was required due to burial by accumulating sand, material weathering, and the use of non-biodegradable components. Despite these limitations, the approach offers insights into how similar systems, potentially constructed from Kiawe wood, could be adapted for short-term erosion control or transitional dune stabilization in Hawai‘i’s coastal settings.
Photo Credit: University of Hawai’i Sea Grant
Photo Credit: University of Hawai’i Sea Grant
Photo Credit: University of Hawai’i Sea Grant
Closed Planting Precedent Study
Location: Paumalū (Sunset Beach), Oahu, Hawai‘i
Strategy: Sand stabilization through protected native plantings
At Paumalū (Sunset Beach) on O‘ahu’s North Shore, a closed planting system was implemented to stabilize coastal sand dunes through native vegetation. According to the North Shore Community Land Trust (2020), approximately 4,000 native coastal plants were outplanted in a grid formation within designated enclosures marked by posts, rope, and educational signage.
To minimize foot traffic and further erosion, specific beach access points were established around these planting zones. The protected environment allowed the vegetation to take root and contributed to the rebuilding of dunes, particularly during calmer summer months.
O ver a two-year period, decreased erosion was documented in the treatment areas, supporting the strategy as an ideal long-term solution for coastal conditions in the Hawaiian Islands. This precedent underscores the importance of controlled access and vegetation management, offering a viable complement to structural methods such as Kiawe-based dune barriers.
Photo Credit: Alice Terry
Photo Credit: Dolan Eversole
Photo Credit: Alice Terry
07 Pāpōhaku
Incorporating Kiawe into site elements at Pāpōhaku Beach Park
A shower station supported by a kiawe wood trunk reflects the rustic and minimalist character of the beach park site.
SECTION A-A
SECTION C-C
SECTION B-B
Creating a Cultural Learning Space
Ka Hula Piko
Pāpōhaku Beach Park is home to Ka Hula Piko, an annual cultural event founded in 1991 by Kumu Hula John Ka‘imikaua, Hālau Hula O Kukunaokala, and the Moloka‘i community (“Moloka‘i Ka Hula Piko: A Celebration of the Birth of Hula on Moloka‘i” 2011). Held every third weekend in May, Hula Piko celebrates the sacred origins of hula in the district of Ka‘ana, West Moloka‘i, widely regarded as the birthplace of hula (“Moloka‘i Ka Hula Piko: A Celebration of the Birth of Hula on Moloka‘i” 2011). The festival honors Laka, the deity associated with hula and the first woman of dance, who is said to have shared this sacred knowledge with the people (“Moloka‘i Ka Hula Piko: A Celebration of the Birth of Hula on Moloka‘i” 2011).
O ver the course of three days, the event brings together residents and visitors for hula performances, traditional music, food, crafts, and educational workshops. Unlike many commercial festivals, Ka Hula Piko maintains a distinctly local and participatory atmosphere. All vendors are from Moloka‘i, and attendees are encouraged to engage deeply with cultural practices rather than passively observe them.
The proposed design at Pāpōhaku Beach Park aims to enhance and support Ka Hula Piko by creating a permanent, outdoor cultural learning and performance space. Centered around a dedicated hula mound, the design integrates Kiawe wood as a primary material, linking ecological restoration with cultural revitalization. Kiawe, often viewed as an invasive species, is reimagined here as a meaningful construction material that can support community gatherings and cultural education.
The design serves not only as an infrastructure upgrade for the event, but as a year-round resource for intergenerational learning, storytelling, and connection to place. In doing so, it aligns with the project’s larger thesis: transforming an ecological challenge into a community asset, and honoring Moloka‘i’s cultural heritage through adaptive, site-responsive design.
Woodchip Mulch
Log Seating
Biochar Cement Pavers
Biochar Cement Stairs
7-8’ High Kiawe Deer Fence
Plant Species for On-site Cultural Practices
Olopua Nestegis sandwicensis Lama Diospyros sandwicensis
• Adze handles
• Digging sticks
• Fishhook rasps
• Hale construction
• Preferred firewood
Kāwelu Eragrostis variabilis
• Movement in wind associated with hula dances
• Reduces surface runoff
• Weed supression
Naio Myoporum sandwicense
• Aromatic firewood
• Hale construction
• Netting needles and gauges
• Edible fruit
• Fish traps
• Hale construction
• Symbol of Laka, goddess of hula
• Torches
Kiawe Prosopis pallida
• Deer fenceposts
• Outdoor live-edge furniture
• Preferred firewood
• Woodchip mulch
Dondonaea viscossa
• Hale construction
• K apa dye
• Lei making
• Topical medicine
Photo Credit: Various Online Sources (Plant Bubbles)
Kiawe Biochar
What is Biochar?
At the Pāpōhaku Beach Park campsite, Kiawe is reimagined as more than an ecological threat. It becomes a locally sourced material supporting cultural use, environmental stewardship, and design innovation. One application developed for this capstone is the use of Kiawe-derived biochar in concrete firepits intended for communal use, during weekend gatherings or for large multi-day events like the Ka Hula Piko. These firepits are designed to support daily park users and overnight campers while modeling sustainable practices through the repurposing of invasive biomass.
Biochar is a carbon-rich material produced through pyrolysis, heating organic biomass in a lowoxygen environment. It is commonly used for soil improvement and carbon sequestration, but recent studies suggest biochar also has potential as a partial replacement for sand in concrete (Praneeth et al. 2020, 1).
This prototype shown on the right advances that idea by using finely processed Kiawe biochar as a full replacement for sand. The mix combines Portland cement blended with lime, locally sourced basalt gravel,
Admix Recipe
• 1 Part Portland with Lime Cement
• 1/2 Part 3/4” Basalt Gravel
• 1 Part Fine Kiawe Biochar
• 1/2 Part Water (or less, as needed)
and fine Kiawe biochar, with water added in small, controlled amounts to maintain workable consistency. The result is a lightweight concrete that retains the basic structural performance necessary for site furnishings like firepits while incorporating high levels of reclaimed material.
Preliminary research indicates that the use of biochar in concrete can offer multiple environmental and mechanical advantages. Studies have found that replacing just 10 percent of sand with biochar can reduce thermal conductivity by over 25 percent, making firepit surfaces cooler to the touch and safer in public spaces (Praneeth et al. 2020, 1). Increasing biochar content to 20 percent has been shown to enhance flexural strength by a similar margin, while 40 percent content may reduce both density and net carbon emissions by approximately 20 percent (1). These characteristics make biochar concrete particularly well suited to low-load applications in coastal parks, where weight reduction, thermal insulation, and environmental performance are valued.
Nevertheless, several limitations must be acknowledged. The long-term durability of Kiawe
biochar-based concrete under conditions typical of coastal exposure, such as salt spray, UV radiation, and variable moisture is not yet fully understood. Additionally, the mechanical integrity of concrete containing high Kiawe biochar content may vary depending on feedstock consistency, particle size, and the specific pyrolysis method used in production. These variables can affect not only strength and density but also chemical interactions within the cementitious matrix. As such, further material testing is essential to refine the formulation and validate its performance under field conditions. Despite these uncertainties, the integration of Kiawe biochar concrete into the design of Pāpōhaku Beach Park’s campsite reflects the central goals of this project: to transform invasive species into material assets and to support culturally and ecologically informed site development.
Kiawe Wood
4’6”
24”
Wood Bench
In addition to the biochar concrete firepits, the campsite design incorporates custom-crafted benches made from solid Kiawe wood slabs. These live-edge benches are intended to provide both functional seating and a material connection to the surrounding landscape. By preserving the natural contours of the wood’s outer grain, each bench reflects the rugged, weathered character of West Moloka‘i’s coastal environment while reinforcing the design ethos of using local, site-responsive materials.
Kiawe wood is well known for its density, durability, and striking coloration. These benches showcase those characteristics through the application of a dark walnut stain that deepens the wood’s natural orangered hues. A spar varnish finish is also used to enhance long-term weather resistance in coastal settings, offering protection from UV exposure, moisture, and microbial growth. In addition, the benches are designed with a slightly elevated seat height to provide a comfortable perch for visitors, whether they are gathering around the firepit or taking in the views of the hula mound from a distance.
By utilizing milled Kiawe slabs, the project extends the tree’s value beyond firewood or waste, instead offering a durable, aesthetically resonant product that enhances the user experience and supports recreational gatherings. Like the biochar concrete, the Kiawe bench installation exemplifies how invasive species can be repurposed into lasting public infrastructure that is ecologically accountable, materially expressive, and culturally grounded.
07 Conclusion
Recapping the existing and potential uses of Kiawe in Hawai‘i
A sample of finely ground Kiawe biochar, produced by burning locally sourced wood on Moloka‘i and ground using a Vitamix blender.
Conclusion
This capstone project demonstrates how an invasive species can be reimagined not simply as an ecological threat, but as a regenerative resource embedded within a culturally and environmentally grounded design framework. Kiawe (Prosopis pallida), introduced to Hawai‘i in the 19th century and now widespread across the islands’ dry lowlands, offers a unique opportunity to address landscape degradation while supporting innovative and community-centered uses.
Across two ecologically sensitive sites, Pāpōhaku Beach Park and Mo‘omomi Beach Nature Preserve, this project explores how Kiawe can be harnessed to restore degraded landscapes, support cultural practices, and reduce environmental impact. At Mo‘omomi, Kiawe is proposed as a structural component in coastal dune stabilization, drawing from nature-based precedents such as post fencing, log trapping, and stake thatching. These hybrid techniques, when paired with native vegetation and community engagement, promote dune resilience without resorting to hard infrastructure.
At Pāpōhaku Beach Park, the approach is both restorative and celebratory. Kiawe wood is repurposed into log seating that shape the Ka Hula Piko stage and cultural workshop space, while woodchip mulch improves site comfort and soil health. In addtion, biochar produced from Kiawe is integrated into a concrete admixture for firepit construction in the campsites, offering a low-carbon, sand-free material alternative. In addition, these campsites are fitted with live-edge Kiawe benches. Altogether, these interventions reduce reliance on imported resources and recenter local materials within culturally meaningful contexts.
A newly proposed test planting area within a vacant field on-site further extends the project’s vision for ecological renewal. Designed as a fenced-in lot using Kiawe wood to deter axis deer, the space is left unpaved to preserve its permeability while functioning as overflow parking during large events like Ka Hula Piko. More importantly, it serves as a demonstration garden for native trees that hold cultural significance to Native Hawaiians through their use in traditional construction, crafts, and symbolic associations, such as hula. This space not only begins to address the site’s existing Kiawe monoculture, but also educates and invites the community to reengage with endemic plant life.
Across all interventions, Kiawe is repositioned from nuisance to necessity, from a source of ecological disruption to a driver of cultural and environmental resilience. Uses explored in this project range from traditional applications like imu construction, fencing, and firewood, to contemporary innovations such as biochar concrete, livestock feed, sand dune stabilization, and soil restoration. The material’s versatility underscores its potential to meet the challenges of invasive species management through adaptive reuse. Ultimately, this project encourages a broader reconsideration of invasive species within design, conservation, and cultural practice. Rather than treating Kiawe solely as a problem to be eradicated, it is reframed as a material and ecological opportunity, one capable of supporting landscape restoration, cultural vitality, and climate-adaptive infrastructure grounded in place.
“Pipi ka wahie, ho’onui ka pulupulu” (If the firewood burns slowly, use more tinder)
- Reverend Henry P. Judd
Do not give up because of a first failure.
Recap of Kiawe Uses in Hawai‘i
Photo Credit:
08 Bibliography
A compilation of sources used for research
A lone kiawe tree established near a rocky Hawaiian shoreline.
Photo Credit: United States Department of Agriculture
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